1. Field of the Invention
The present invention relates to a method of fabricating a thin film transistor and the thin film transistor.
2. Background of the Related Art
An inverse staggered type thin film transistor (hereinafter abbreviated TFT) is widely used for a thin film transistorxe2x80x94liquid crystal display (hereinafter abbreviated TFT-LCD) panel. A metal is deposited on a glass substrate for the inverse staggered type TFT. However, reliance of the device is reduced due to a difference between the thermal expansion coefficients of metal and glass as well as stress, which results in metal peeling. In most cases, a gate metal is deposited on a buffer layer, which has been formed on the glass substrate. Silicon nitride and silicon oxide are widely used as the buffer layers. Yet, such a buffer layer can only be used when the adhesion of the metal is excellent. Thus, some metals fail to overcome the above defects. Stacked-metal structures have been proposed to overcome such defects and contribute greatly to metal diffusion and adhesion improvement. However, these proposed structures fail to avoid reductions in productivity. Another metal mixing method fails to reduce resistance due to the metal mixtures.
As the size of a TFT-LCD panel increases, metals having low resistance are required. Cu(1.67 xcexcxcexa9.cm) and Agxe2x80x94Pdxe2x80x94Cu alloy (hereinafter abbreviated APC) (under 2.2 xcexcxcexa9.cm) have low resistance, but they have unstable properties such as poor adhesion with the glass substrate. Namely, adhesion of Cu is poor. Cu also has a tendency to diffuse into a silicon film and has to be mixed with other metals such as Cr, Mg or/and the like, thereby increasing the resistance thereof. Compared to Cu, APC has no tendency to diffuse into a silicon film, but has poor adhesion, thereby failing to avoid the film peeling problem.
Moreover, metals having low resistance such as Cu, APC and the like are vulnerable to deformation due to their weakness. Specifically, in a plasma process for depositing a film, characteristic degradation such as roughness and resistance of such metals and the like are increased due to a reaction between the metals and the gas. And, metal diffusion occurs in the plasma process due to the process temperature. To overcome these problems, a buffer layer is formed on the metal. This process is divided into three methods, one using stable metals such as Mo, Cr, W, and Ti, one using an oxide layer such as Cr2O3 and Al2O3 by thermally treating the metals, and one using a nitride layer such as AlN and TiN by carrying out thermal treatment in a nitrogen ambient atmosphere. Also these methods of using a metal film need to carry out photolithography twice to pattern the metal for securing a stable buffer state, thereby complicating the formation process.
Accordingly, the present invention is directed to a method of fabricating a thin film transistor using a buffer layer that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method of fabricating a thin film transistor and a thin film transistor using a buffer layer so as to reduce the deformation of a metal having weak resistivity when depositing a film.
Another object of the present invention is to provide a method of fabricating a thin film transistor and the thin film transistor using a buffer layer, thereby improving adhesion of low resistance metals used for TFT gate metals.
In the present invention an aluminum oxide or nitride layer is deposited to use as a buffer layer. The aluminum oxide layer is formed by oxygen plasma treatment using PECVD (Plasma Enhanced Chemical Vapor Deposition) so as to form an alumina layer having no impurity instantly. And, the aluminum nitride layer is formed using RF magnetron sputtering. A metal gate is then patterned on the buffer layer. The buffer layer improves the adhesion between the glass substrate and the gate metal. In further preferred embodiments, a second aluminum oxide layer or aluminum nitride layer, as a second buffer layer, is formed over the metal gate and the first buffer layer. The second buffer layer helps prevent the deformation of the metal gate during the subsequent processing step to form the TFT that includes the metal gate.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.